I have a buy-button image set in all posts on the entire site. When permalink settings are default the URL to that image file is www.mydomain.com/images/buy-button.gif. When permalink settings are custom the URL to that image file is generated dynamically to www.mydomain.com/permalinkcustom/images/buy-button.gif. The result is that the buy button is not visible any more on the posts as its URL remains the same as if when permalink settings is still default. How can I configure this URL-rewrite?